The present invention relates to a device for separating selected fractions of liquids, with particular regard to the fractions arising in density gradient centrifugation.
In the process of density gradient centrifugation, a density gradient of the liquid is formed and the various materials are localized in distinct layers of the liquid. After centrifugation, the gradient should be fractionated, for which purpose different techniques are used. A generally applied method, for example, is to collect the fractions from the top or bottom of the tube by suctioning off the liquid layer. For detailed discussion of the fractionation techniques, see the literature: "Preparative density centrifugation", Beckman Instrument International S.A., Geneva /1975/, Fritsch. A.
The known techniques of gradient fractionation can only partially satisfy the ideal requirement that the layers of liquid fractions be separated in thin, horizontal layers that do not undergo mixing during the separation process, and the further requirement that the process be quick enough for routine laboratory work in large series.
A new technique has recently been published in which gradient fractionation is carried out in a multi-chamber ultraeentrifuge tube. This tube is made from plastic material, and the chambers of the tube are joined by a constricted area which permits fluid communication between the chambers. Subsequent to centrifugation, the chambers can be sealed from each other to retain the separated fractions of the liquid. /See: PCT patent application, PCT International Publication Number WO 84/00313, priority U.S. application Ser. No. 395,371, now U.S. Pat. No. 4,511,349.
In spite of the present developments, further progress in this field is desirable as the gradient centrifugation technique is an important, widely used laboratory method. As examples, this method nowadays finds important application in medical diagnosis, serum lipoproteins can be separated and charactertized by density gradient centrifugation, and by measuring the quantities of cholesterol in the separated lipoprotein fractions, valuable information can be obtained with respect to prediction of the risk of coronary heart disease.